Evolution Gun Works Plunger Tube Spring Silicone Chrome. This prevents the slide stop from bouncing up prematurely and gives the thumb safety a secure feel.All ISMI Springs are made from silicone chrome instead of 150 year old music wire. Every ISMI spring is heat treated shot peened & stress relieved to enhance durability consistency and reliability. ISMI is a contractor of the U.S. government and produces springs used in machine guns with incredibly high cycling rates. Also the creator of ISMI springs obtained his knowledge from extensive research in the development of springs used in Indy car racing. Specifications for Evolution Gun Works Plunger Tube Spring: Manufacturer: Evolution Gun Works Color: Chrome Fabric/Material: Silicone Package Contents: Evolution Gun Works Plunger Tube Spring Evolution Gun Works 10680: Plunger Tube Spring Silicone Chrome